Catalytic imide compounds such as N-hydroxyphthalimide receive attention as catalysts that can allow various reactions to proceed smoothly under mild conditions. Such reactions include, for example, oxidation with molecular oxygen, carboxylation, nitration, sulfonation, acylation, and radical coupling reactions.
For example, Japanese Unexamined Patent Application Publications No. 08-38909 and No. 09-327626 each disclose a process for oxidizing a substrate, such as a hydrocarbon or an alcohol, with molecular oxygen in the presence of an imide compound catalyst to thereby yield, for example, a corresponding alcohol, aldehyde, ketone, and/or carboxylic acid. Japanese Unexamined Patent Application Publication No. 09-278675 discloses an oxidation process of a conjugated compound using the imide compound catalyst. Japanese Unexamined Patent Application Publication No. 10-316610 describes that esters, acid anhydrides, lactones or other products are formed by oxidizing ethers in the presence of the imide compound catalyst. PCT International Publication No. WO 99/50204 discloses a process for producing a corresponding epoxide by oxidizing a compound having a non-aromatic ethylene bond with molecular oxygen in the presence of the imide compound catalyst and a co-oxidizing agent, and a process for producing a corresponding ester or lactone by oxidizing a ketone with molecular oxygen in the presence of the imide compound catalyst and the co-oxidizing agent.
Japanese Unexamined Patent Application Publication No. 11-239730 discloses a process for producing a corresponding nitro compound by allowing a substrate to react with a nitrogen oxide in the presence of an imide compound catalyst, and a process for producing a corresponding carboxylic acid by allowing a substrate to react with carbon monoxide and oxygen in the presence of the catalyst. PCT International Publication No. WO 99/41219 mentions that an acylation reaction of a substrate with oxygen and a 1,2-dicarbonyl compound such as biacetyl in the presence of the imide compound catalyst can proceed under mild conditions. The Chemical Society of Japan, Spring Annual Meeting, Lecture Proceedings (1999) reports that a radical coupling reaction of an α, β-unsaturated ester with an alcohol and oxygen proceeds by catalysis of N-hydroxyphthalimide and thereby yields an α-hydroxy-γ-butyrolactone in a good yield. The Lecture Proceedings also reports that a reaction of a hydrocarbon such as adamantane with oxygen and sulfur dioxide by catalysis of N-hydroxyphthalimide yields a corresponding sulfonic acid.
As is described above, the imide compound catalysts are very useful as catalysts for wide variety of organic synthesis reactions such as oxidation reactions. However, few reports have been made on a method for separating a reaction product from the imide compound catalyst after the completion of the reaction. For example, Japanese Unexamined Patent Application Publication No. 10-114702 discloses a method for separating a reaction product from an imide compound catalyst in an oxidation reaction mixture obtained as a result of a reaction using the imide compound catalyst. The method includes the steps of using an aqueous solvent containing at least water and a water-insoluble solvent separable from the aqueous solvent and dividing the oxidation reaction product into the aqueous solvent layer and the oxidizing catalyst into the water-insoluble solvent layer. However, this method cannot significantly separate a water-insoluble reaction product from a water-insoluble or water-soluble catalyst, although it can be an effective means for separating a water-soluble oxidation reaction product from a water-insoluble catalyst.
The imide compound catalyst may be partially altered after a reaction under some conditions. If a decomposed product or another altered derivative of the catalyst contaminates an end product of the reaction product, it may deteriorate the quality of the end product. However, no separation method for such altered derivatives has been known.